| Nanotechnology was of priority development in science and technology revolution,widely used in medicine industry,electronic industry,chemical biological engineering,and other fields.In recent years,nanomaterials are directly or indirectly discharged into the environment,and eventually entered the sewage treatment plant.Therefore,a series of environmental risks caused by them have attracted extensive attention from the society.However,the effects of short-term and long-term exposure of nanomaterials on wastewater treatment efficiency and microbial community dynamics in activated sludge systems are lack systematically studied.Therefore,in this study,the nano-Fe3O4,one of the most common nanomaterials was selected as research object.The enzymology,spectroscopy and high-throughput sequencing was employed to investigate the mechanism of short-term and long-term exposure of nano-Fe3O4 to treatment efficiency and microbial community dynamic structure on activated sludge system.Firstly,the effect of short-term exposure to nano-Fe3O4 on the treatment efficiency of activated sludge system was investigated by batch flask shaking experiment.The results showed that low concentration of nano-Fe3O4 could promote the degradation efficiency of phenol and COD,but when its concentration was over 600 mg/L,the degradation efficiency of phenol and COD was inhibited in the activated sludge system.Meanwhile,the detection of intracellular ROS and lactate LDH indicated that high concentration of nano-Fe3O4 exposure would cause oxidative stress reaction in microbial cells,which led to destruction of the integrity of cell membrane,affected the physical and chemical properties and physiological functions of the activated sludge system.In addition,compared with the system containing EPS,the degradation efficiency of phenol and COD and the content of ATP in the activated sludge system were both reduced after removing EPS under the same concentration of nano-Fe3O4,which indicated that the presence of EPS in the activated sludge protected microorganisms from the toxic effect of nano-Fe3O4.As mentioned above,we took SBR system as the research object to investigate the effect of long-term exposure of nano-Fe3O4 on the treatment efficiency of SBR system.The degradation efficiency of phenol in each system reached 100%during the whole operation period.When the concentration of nano-Fe3O4 increased from 0 to 600 mg/L,the COD removal efficiency was significantly improved,and when the concentration was higher than 600 mg/L,the COD removal efficiency was significantly reduced.Enzyme activity analysis showed that the contents of key enzymes and ATP in SBR system were significantly increased when exposed to low concentration of nano-Fe3O4,and significantly decreased when the nano-Fe3O4 concentration were higher than 600 mg/L.The analysis of extracellular polymer(EPS)content showed that the protein(PN)and polysaccharide(PS)contents in EPS were significantly reduced when exposed to low concentration of nano-Fe3O4 and the contents of PN and PS in EPS were increased when the nano-Fe3O4 concentration were higher than 600 mg/L,which further proved the protection mechanism of EPS in SBR system.In addition,the UV-Vis spectrum,FTIR spectrum and 3D-EEM spectrum analysis showed that low concentration of nano-Fe3O4 exposure,the number of functional group of soluble microorganisms metabolize protein substances,humic acid,C=O,-NH2,C-N,C-O-C associated with PN,C-O,C-OH associated with PS and O-P-O associated with nucleic acid in EPS were gradually reduced when exposed to low concentration of nano-Fe3O4 and the number of functional groups above were increased when the nano-Fe3O4 concentration were higher than 600 mg/L.At the same time,the effects of long-term exposure of nano-Fe3O4 on microbial community toxicity and structural dynamics were investigated.LDH and ROS tests showed that the exposure of low concentration nano-Fe3O4 had no toxic effect on SBR microorganisms and the exposure of high concentration of nano-Fe3O4 would cause toxic effect on microorganisms in activated sludge system and destroy the integrity of microbial cell membrane in SBR system.High-throughput sequencing further demonstrated that long-term exposure to nano-Fe3O4 significantly altered the composition and structure of microorganisms in the SBR system.Exposure to low concentration of nano-Fe3O4 significantly enhanced the diversity and richness of microbial community,promoting the growth of dominant bacteria such as OLB8,Pseudomonas,Rhodanobacter,Bacillus,Luteococcus,Devosia and Comamonas and the microbial community diversity and richness would be inhibited under the high concentration of nano-Fe3O4 exposure,which inhibited the growth of the bacteria.In addition,DCA analysis showed that long-term exposure of nano-Fe3O4 was an important factor affecting microbial community changes in SBR system. |
PDF Full Text Request